Oscillators are circuits for converting dc power into a periodic waveform or signal. Conventional RC oscillators advantageously furnish a low-cost timing source and allow for generation of variable frequencies by changing the resistance R, or capacitance C. Furthermore, conventional RC oscillators advantageously avoid the use of inductors, which are difficult to fabricate on integrated circuits.
It is inherent in an oscillator that a lengthy interval transpires before the oscillator timing reaches a stable operating frequency following application of operating power. This characteristic is inherent in all oscillators, such as high Q LC oscillators or extremely high Q crystal oscillators, for example. In LC oscillators and crystal oscillators, slow stabilization results from the high Q of the oscillator circuit.
In laptop computers and low power computers, a power-down mode is an important feature to conserve power, particularly in battery-powered operation. In the power-down mode, power is not completely removed from a microprocessor chip. Rather the chip is left enabled but is placed in an idle state in which little power is consumed. A large amount of power is conserved in power-down mode by deactivation of the oscillator. However, a problem arises when power-down mode ends. If the oscillator takes too long to stabilize, the user of a laptop or low-power computer may perceive the slow response as an error in a function controlled by the oscillator. Therefore, it is highly advantageous to furnish a capability to respond quickly during recovery from power-down mode.